Biological Molecules: Polysaccharides

Question 1

Starch: Monomers & Polymers

Answer 1

• Monomer - α-glucose
• Polymers - amylose and amylopectin

• Amylose

• Alpha (1-4) glycosidic bonds
• Long, unbranched chains of α-glucose
• Hydrogen bonds help hold the α-glucose in its helical structure

• Amylopectin

• Alpha (1-6) glycosidic bonds
• Long, branched chain of α-glucose

Question 2

Starch: Function

Answer 2

• Function - energy store for plants

- Found in grains in plant cells, especially in seeds and storage organs

Question 3

Starch: Specialisation

Answer 3

• Insoluble - won’t affect water potential
• Compact - more glucose stored in a smaller volume

• Amylose

• Helical and unbranched shape makes it compact
• Hydrogen bonds help hold the α-glucose in its helical structure

• Amylopectin
- Many side branches that can be acted upon simultaneously by many enzymes and thus quickly hydrolysed to release its energy

Question 4

Test for Starch

Answer 4

• Add iodine solution to sample

- If starch is present, solution will turn from orange/brown to blue/black

Question 5

Glycogen: Monomers & Bonds

Answer 5

• Monomer - α-glucose

- Polymers of α-glucose with (1-4) and (1-6) glycosidic bonds

Question 6

Glycogen: Function & Specialisation

Answer 6

• Main energy storage molecule in animals
• Found in mammalian muscles and liver
• Large number of side branches, glucose is released quickly by hydrolysis
• Large but compact molecule thus maximising the amount of glucose it can store - good energy source
• Insoluble - will not affect the water potential of cells and cannot diffuse out of cells
• Glycogenesis - making glycogen from glucose

Question 7

Cellulose: Monomers & Bonds

Answer 7

• Monomer - β-glucose

- Polymers of β-glucose with (1-4) glycosidic bonds

Question 8

Cellulose: Function & Specialisation

Answer 8

• Forms cell walls in plant cells

• Microfibrils

• Strong threads made of long parallel cellulose chains that are joined together by hydrogen bonds, forming strong cross linkages
• Parallel chains are made by flipping every other β-glucose molecule 180 degrees, allowing them to form hydrogen bonds with other chains

• Insoluble

• Effective barrier
• Stops the cell from bursting under osmotic pressure
• Exerts inward pressure that stops the influx (flow) of water. Cells stay turgid and rigid, helping to maximise the surface area of plants for photosynthesis